In the SM, the low energy effective Hamiltonians for \(b\rightarrow s/d\ell ^+\ell ^-\) , \(c\rightarrow u\ell ^+\ell ^-\)  and \(s\rightarrow d\ell ^+\ell ^-\)  FCNC transitions have similar forms and can be written as [1]}, [2]}, [3]}, [4]}, [5]}
\(\mathcal {H}(q_1\rightarrow q_2\ell ^+\ell ^-)=-\frac{\alpha _eG_F}{\sqrt{2}\pi }\lambda _{q_1q_2}\left(C^{eff}_9\bar{q}_2\gamma ^\mu P_L q_1 \bar{\ell }\gamma _\mu \ell +C_{10}\bar{q}_2\gamma ^\mu P_Lq_1 \bar{\ell }\gamma _\mu \gamma _5\ell -\frac{2m_{q_1}}{q^2}C^{eff}_7 \bar{q}_2iq_\nu \sigma ^{\mu \nu }P_R q_1 \bar{\ell }\gamma _\mu \ell \right),\) 
